April Fools' Day history? Be wary of those who say they know.

April Fools' Day history is murky, and nobody knows its origins. So beware any Boston University professors who claim it originated in the court of Constantine.

Here's no joke: Nobody knows the origins of April Fools' Day.

Some speculate that Europe's switch from the Julian calendar to the Gregorian in the 1500s, which changed New Year's Day from late March to Jan. 1, created an easy opportunity to play a prank on the forgetful. But that wouldn't explain why April Fools' Day is mentioned even earlier in writing, in Chaucer’s 14th-century "Canterbury Tales."

Other theories abound, but every year the people want to know: What is the history of April Fools' Day?

And every year the media respond: We don't fully know.

One year, a reporter from the Associated Press pushed so hard for an answer that he fell victim to one of the bigger April Fools' Day pranks in American history.

Back in 1983, Boston University Prof. Joseph Boskin got a call from the press relations office asking what he knew about April Fools' Day. "I said [sarcastically] I'd been researching it for years," Dr. Boskin recalled Thursday, in a telephone interview from his home in Cambridge, Mass.

Days later, he was flying to Los Angeles to interview Norman Lear, producer of "All in the Family," to write a history of the television show. When his flight landed, the airport intercom called his name, telling him to go to the nearest white phone. It was BU's press relations office again, saying it had set up an interview between him and the Associated Press to talk about the history of April Fools' Day.

"I said, 'You know, I was just jiving,' " Boskin recalls. "I protested and said I couldn’t do it. She said, 'Oh no, you must call him.' "

Later that day, Boskin got on the phone with an AP reporter in New York City. "I said, 'I know nothing about April Fools' Day.' And the reporter said something like, 'You’re being modest.... What are the origins?' "

Boskin relented, spinning a yarn that the holiday originated in Istanbul in the court of Constantine when "the jesters decided to unionize." The king was so amused that he agreed to give up the throne to a jester for the day. The first-ever April fool was Kugel (Boskin thought of the name because his friend especially enjoyed the Jewish pudding), who declared it a day of absurdities.

"All I could hear in the background was click, click, click," Boskin says, mimicking the sound of the reporter's clacking typewriter. After the AP printed the story, Boskin got calls from the "Today" show and newspapers around the US and Canada. Only weeks later, in one of his history classes, did he reveal the hoax to his students. Unbeknown to Boskin, the school newspaper's editor in chief was in the class, and the professor's confession appeared on the front page the next day.

BU's press office and the AP were livid, Boskin says. He kept his job only because he had tenure. The wire service's New England bureau chief accused him of ruining the life of a young reporter, and the reporter himself called Boskin in tears.

"The New England chief accused me of lying.... I accused the AP of being sanctimonious. Rather than blame themselves [for failing to fact-check], they took it out on me. They sent out a story: 'Professor lies about April Fools Day.' "

While the media in this case didn't appreciate the hoax, the media have a history of pulling pranks on the public on April 1. In 1965, the BBC interviewed the inventor of “smellovision,” which purportedly allowed viewers to smell whatever was on TV (it really was invented for movies). Today, British media reported that William Shakespeare was half French and that someone had invented the flavored headline.

Boskin finally buried the hatchet on his 1983 April Fools' Day joke last year, when he had lunch with the AP reporter. As it happened, the reporter had become a fellow professor at BU.

"I've written three or four books, [and] many articles," Boskin says, "but this seems to be my Andy Warhol moment, a spontaneous story about Kugel."